Radiation curable phase change gel inks may be used to form images on substrates in printing. The ink may be exposed to radiation to cure the ink. Exemplary radiation-curing techniques include, but are not limited to, curing using ultraviolet (UV) light, for example having a wavelength of approximately 240-450 nm or more rarely visible light, optionally in the presence of photoinitiators and/or sensitizers, curing using thermal curing, in the presence or absence of high-temperature thermal initiators (and which may be largely inactive at the jetting temperature), and appropriate combinations thereof.
During this exposure, photoinitiator substances contained in the ink may be irradiated with the UV radiation, and the incident flux converts monomers in the ink into a cross-linked polymer matrix, resulting in a hard and durable mark on the substrate. For some applications, it may be desirable to spread or level the ink on the substrate before curing. Leveling can produce more-uniform image gloss and mask missing jets of print heads. Additionally, certain print applications, such as packaging, may benefit from having thin ink layers of relatively constant thickness in prints.
UV curable inks are used for many applications for which a durable printed image is desired, such as packaging applications. An important class of UV curable inks includes acrylate monomers, oligomers, specific photoinitiators, and other components that react chemically when exposed to UV light energy and form a polymerized, cross-linked, durable image. This curing process is applied to UV curable images formed by, for example, flexography, offset, and inkjet systems.
In related systems, a flood mercury arc lamp is used to irradiate and cure UV ink images during printing. The mercury lamps may be doped variously with, e.g., iron or gallium. These lamps are expensive, typically costing $15,000 or more depending on width and manufacturer as of the filing date of this application. Moreover, such lamps waste energy during a print job by illuminating an entire image area on a substrate, including areas that do not include ink to be cured. The lamps emit light at high power in a broad spectrum of frequencies, most of which are not beneficial to the curing process. At high printing speeds, multiple lamps are used. A power needed to cure the ink is set high enough to cure the most difficult-to-cure color of ink or thickest layer of ink.